Dioxin alters ability to fight infection, mouse study finds.

Context

Dioxins are a family of structurally related chemicals. They are mainly produced as byproducts during manufacturing processes and the burning of garbage, medical wastes and other materials. Dioxins cause cancer, affect reproduction and development and harm the immune system. Health symptoms noted after workplace and accidental exposures include skin rashes called chloracne, tiredness and metabolic changes.

Dioxins are persistent organic pollutants; once released into the environment they degrade slowly, if at all. The chemicals can travel in the atmosphere and return to Earth with rain and snow. They may land in water, on land or on plants and travel up the food chain, where they eventually bioaccumulate in people and other top predators.

The main route of human exposure is through diet, particularly fatty ones rich in red meat and dairy products. A low-fat diet is one way to reduce exposure. A diet rich in vegetables not only lessens dioxin exposure but may also counteract its harmful effects. Compounds found in certain foods, such as broccoli, cauliflower and green tea, have been found by cell and animal studies to limit, and in some cases, antagonize dioxin's effects.

Dioxin levels are typically reported as parts per trillion (ppt), which less than a drop of water in an Olympic-sized swimming pool. Levels of the environmental pollutant have dropped considerably in recent years. Average levels in people are now less than 10 parts per trillion. Levels in more than half of the US population are below detection. Nevertheless, certain "hot-spots" have considerably higher levels. The EPA found that portions of the Saginaw River in Michigan, downstream of a Dow Chemical plant, registered dioxin levels of 1.6 million parts per trillion.

Animals breakdown and eliminate dioxin differently. Mice, for example, can process the pollutant in 7-14 days (for TCDD, the most potent dioxin) whereas humans take 14 years to eliminate the same amount. The faster turn-around in mice makes them good study models for determining dioxin's health effects.

Animal and human epidemiological studies show that dioxin causes a wide variety of health effects, including reproductive problems, skin diseases, cancer and immune suppression. Adult mice given dioxin have a reduced capacity to fight an influenza infection (Lawrence et al. 2000; Warren et al. 2000).

PCBs have chemical properties similar to dioxin, so study results of PCBs are helpful for effects comparisons. An epidemiological study by the Dutch health service correlated child health outcomes to the levels of PCBs in their mother’s breast milk. They found that a higher exposure to PCBs resulted in children being more susceptible to viral ear infections during their early years (Koopman-Esseboom et al. 1996; Weisglas-Kuperus et al. 1995, 2000).
 

This study looked at the long term immune effects of dioxin when exposure occurs during development. The authors tried to identify the critical windows of exposure where fetuses are most sensitive to dioxin's harmful effects.

Pregnant mice were given a dose of 1,000 ppt dioxin either: 1) throughout gestation (days 0, 7 and 14) and lactation (day 2 after birth); 2) gestation only (days 0, 7 and 14); 3) lactation only (day 2); or 4) late during gestation (day 14) and continuing on during lactation (day 2).

After exposure, the pups and their mother’s were kept dioxin free for the rest of their lives. At 8 weeks, the pups and their moms were infected with a non-lethal dose of the influenza virus. One week later, lung tissue was collected and analyzed for the number and types of white blood cells. Inflammation factors produced in the lungs by the white blood cells were measured.